JP2004289788A - System and method for performing symbol boundary-aligned search of direct sequence spread spectrum signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and method for performing symbol boundary-aligned search of direct sequence spread spectrum signals. <P>SOLUTION: A preferred embodiment comprises a search control unit (such as search control unit 725) that can determine a start and stop condition for a correlation based on a hypothesis, a searcher (such as searcher 705) which includes a multiplexer that can select a subset of samples of a received sequence based on the hypothesis and start and stop conditions. The search control unit can then wait for the occurrence of the start condition and assign the hypothesis to a correlator, which will correlate the subset of samples with a locally generated pseudo-random number sequence based upon the hypothesis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to digital wireless communication systems and methods, and more particularly, to systems and methods for performing searches for direct sequence spread spectrum signals where the search is aligned along symbol boundaries.

  In a direct sequence spread spectrum digital wireless communication network, a necessary part of the communication processing of a wireless device is to find a certain signal transmitted by a base station. One example of such a signal is a pilot channel. The wireless device uses a searcher to find a pilot channel for the wireless device. The searcher attempts to achieve synchronization with a base station transmitted pseudo-random number (PN) sequence transmitted on a pilot channel. Synchronization is used for a variety of purposes, including cell selection (used for cell handoff), finger assignment and maintenance (used for multi-path combining to maximize received signal strength). ), Channel profile estimation, location identification, etc.

  Synchronization involves correlating a received signal (eg, a PN sequence transmitted on a pilot channel) with a locally stored version of the PN sequence with adjusted PN offset. The PN offset of the PN sequence, along with other information such as dwell time, window size, etc., is commonly referred to as hypothesis. If the two PN sequences match, then the correlation yields a large value, but the correlation for the two PN sequences that do not match yields a small value. The result of the correlation can then be accumulated or accumulated (coherent or non-coherent). The accumulated value can then be compared against the threshold. If the accumulated value exceeds the threshold, then the hypothesis is declared to be the correct hypothesis. Obtaining the PN offset is essentially acquiring the pilot channel.

  In a direct sequence spread spectrum wireless communication system using orthogonal spreading codes, no interference occurs between transmitted signals as long as orthogonality is maintained. Examples of such wireless communication systems include IS-95 (early CDMA (code division multiple access) communication system standard), CDMA2000 (third generation CDMA communication system standard), and UMTS universal mobile telephone system, also a third generation CDMA communication system standard). In these communication systems, the orthogonality of transmitted signals is maintained along symbol boundaries. This means that if correlated along the symbol boundaries, the uncorrelated signal will not interfere with the desired signal. However, if correlations are taken between symbol boundaries, then orthogonality of the signal is no longer guaranteed and interference will occur.

  Moreover, in direct sequence spread spectrum wireless communication that uses an antenna diversity scheme to help improve performance, typically orthogonality is achieved only when accumulation is performed along slot boundaries. Is guaranteed. For example, if an accumulation crosses one slot boundary, then interference from other transmitted signals may occur and the received signal strength may fluctuate significantly.

  The methods commonly used to search for pilot channels (and other signals) typically involve different samples of the data received at a particular instance (instance) and the pilot channel PN sequence. Correlating the received data samples with the shift (PN offset). This method is easy to implement and requires a minimal buffer of incoming data samples.

  One solution to ensure that accumulation occurs along symbol boundaries is to test and parse a hypothesis that only those that occur along symbol boundaries are tested. is there. Hypotheses that do not result in symbol boundary accumulation are retained until the time those tests occur along the symbol boundaries.

  One disadvantage of the prior art is that the accumulation is aligned to signal boundaries under very few instances. Thus, interference from other transmitted signals may occur, and possibly reduce the signal-to-noise ratio of the communication system, thereby reducing its overall efficiency.

  A second disadvantage of the prior art is that testing only the hypothesis about accumulation aligned with signal boundaries can severely reduce the overall throughput of the searcher. Thus, the synchronization time can be very long, possibly longer than permitted by the network.

  A third disadvantage of the prior art is that forcing the hypothesis to wait until a reasonable time may require a significant amount of buffer space. Therefore, it is to increase the cost and power consumption of searchers and wireless devices.

  These and other problems are generally solved or avoided by the preferred embodiments of the present invention, which provide systems and methods that ensure a search for direct sequence spread spectrum signals that occur along specific boundaries. Advantages are generally achieved.

  According to one preferred embodiment of the present invention, a method for testing a hypothesis by signal alignment correlation includes receiving a hypothesis, determining start and stop conditions, and sampling the received sequence based on the start condition. And providing the samples and hypotheses to the correlator.

  According to another preferred embodiment of the present invention, the circuit includes a search control unit coupled to the hypothesis memory for providing start and stop conditions for hypothesis-based correlation read from the hypothesis memory. A search control unit and a searcher coupled to the search control unit for selecting a subset of samples from the received sequence based on instructions from the search control unit and correlating the subset of samples with the pseudo-random number sequence to obtain a correlation result. A sequencer coupled to the search control unit and the searcher, the circuit including a circuit for accumulating or accumulating the searcher, wherein the sequence generator includes a circuit for generating a pseudo-random sequence based on a hypothesis. Is included.

  According to another preferred embodiment of the present invention, a wireless device comprises an analog front end coupled to an antenna, the analog front end including circuitry for filtering and amplifying a received signal provided by the antenna. An analog-to-digital converter (ADC) for converting an analog signal provided by an analog front end to a digital symbol stream; and a search unit coupled to the ADC for testing a test hypothesis. A search unit including circuitry, wherein the test is performed along a symbol boundary and a processing unit coupled to the ADC, the error detection and correction, record and despread, and the digital symbol Said processing unit for filtering the stream.

  One advantage of the preferred embodiment of the present invention is that the orthogonality of the signals is maintained by performing the accumulation aligned with a particular boundary, and in accumulating the desired signal, there is no difference between these signals. No interference is introduced. Thus, the signal to noise ratio of the system is maximized.

  A further advantage of the preferred embodiment of the present invention is that the implementation of the present invention can be accomplished with little additional cost since the present invention requires little additional hardware.

  Yet another advantage of the preferred embodiment of the present invention is that maximum flexibility can be achieved because it can operate with any dimension of boundary size and accumulation length.

  The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It is readily understood by those skilled in the art that the disclosed concepts and particular embodiments can be readily implemented as a basis for modifying and designing other configurations or processes to accomplish the same purpose of the invention. Let's do it. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

  The manufacture and use of a presently preferred embodiment of the present invention is discussed in detail below. It should be understood, however, that the present invention provides many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific examples discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

  The present invention will be described in terms of a preferred embodiment in a particular context, namely a direct sequence spread spectrum wireless communication system produced according to CDMA (IS-95), CDMA2000 and UMTS (Universal Mobile Telecommunications) technology standards. An overview of the CDMA2000 technical standard is provided in a document entitled "Introduction to CDMA2000 Spread Spectrum System, Release 0," which is incorporated herein by reference. An overview of the UMTS Technical Standards is provided in a document entitled "3rd Generation Partnership Project; Technical Specifications Group Services and System Aspects General UMTS Architecture (Release 4)" Is incorporated by reference. However, the invention is also applicable to other digital wireless communication systems using direct sequence spread spectrum techniques with orthogonal spreading codes.

  Referring now to FIG. 1, a diagram illustrating an exemplary wireless communication system 100 is shown. In this wireless communication system, there is a mobile station 105 communicating with a base station 110. In addition to base station 110, there are multiple other base stations 115, which are farther away from mobile station 105 than base station 110. Since the mobile station 105 was able to synchronize with the signal from the base station 110 when the power was turned on, the mobile station 105 started connecting to the wireless communication system 100 using the base station 110.

  As discussed previously, in a code division multiple access (CDMA) wireless communication system, such as a system according to IS-95, CDMD2000, or UMTS, the mobile station is synchronized with the base station upon power up. It is necessary to This synchronization process requires the mobile station to perform multiple correlations between various offsets of a locally stored pseudo-random number (PN) sequence and the received signal. This correlation also includes the application of various scrambling codes. In addition, mobile stations are required to test received signals at various carrier frequencies.

  Synchronization of a mobile station to a base station is typically performed by a portion of the mobile station commonly called a searcher. The searcher receives as input a received signal detected by the mobile station, usually in the form of a pair I and Q. The searcher then correlates the I and Q sequences with the locally stored PN sequence at a particular offset. This offset is commonly referred to as a PN offset, and the process of correlating a received sequence with a PN sequence is commonly referred to as testing a hypothesis.

  Referring now to FIG. 2, there is shown a timing chart illustrating several bit periods of signals that may be used for direct sequence spread spectrum communication with orthogonal spreading codes. The first curve 205 represents the signal carried on the pilot channel, while the second curve 210 represents the signal carried on channel S1, and the third curve 215 represents the signal carried on channel S2. Displays the signal being carried. Note that channels S1 and S2 are spread using orthogonal spreading codes, and that these spreading codes are orthogonal on a bit-wise basis, as shown in FIG. This implies that the signals on channel S1 and channel S2 do not interfere with each other when bit-aligned accumulation occurs. FIG. 2 shows bit I of the signal on channels S1 and S2 (interval 220 and bit I + 1 (interval 225) and the pilot channel are shown).

  Some highlights illustrate exemplary accumulation intervals for the pilot channel. The first accumulation of the pilot channel (highlight 230), aligned to the signal bits on channels S1 and S2, preserves the orthogonal nature of these signals. Therefore, the signals on channels S1 and S2 have no effect on the accumulation of the pilot channel. The second accumulation of the pilot channel (highlight 235) starts shortly after the start of bit I (interval 220) and ends shortly after the start of bit I + 1 (interval 225). Therefore, the orthogonality of the signals on channels S1 and S2 is not maintained, and the signals on channels S1 and S2 appear as noise in the accumulation of the pilot channels. The third accumulation of the pilot channel (highlight 240) starts shortly before the end of bit I (interval 220) and ends shortly before the end of bit I + 1 (interval 225). Again, since the accumulation is not bit aligned again, the orthogonality of the signals on channels S1 and S2 is not maintained and they appear as noise in the accumulation.

  Referring now to FIG. 3, there is shown a timing chart illustrating modulation patterns for a direct sequence spread spectrum communication system using transmit antenna diversity. FIG. 3 shows a part of the transmission pattern at the end of the transmission frame I (interval 315) and a part of the transmission pattern at the start of the transmission frame I + 1 (interval 320). One transmission frame includes fifteen transmission slots labeled slot # 0 through slot # 14, each slot being of the same duration (interval 325). As shown in FIG. 3, the direct sequence spread spectrum communication system uses two transmission antennas (the transmission pattern of antenna 1 is displayed as pattern 305 and the transmission pattern of antenna 2 is displayed as pattern 310). Then, a space-time transmission diversity scheme is implemented.

  The first accumulation (indicated as highlight 330) is aligned with the transmission slot (slot # 0), thus preserving the orthogonality of the transmission diversity scheme. Since the second accumulation (highlight 335) and the third accumulation (highlight 340) are not aligned with the transmission slots, the orthogonality of the transmission diversity scheme is lost. The effect of the loss of orthogonality of the transmit diversity scheme is seen in the received signal strength, as discussed below.

  Referring now to FIG. 4, there is shown a data plot illustrating normalized coherent accumulated energy as a function of normalized symbol boundary offset. FIG. 4 illustrates the normalized accumulated energy of several different accumulated lengths (shown as various curves) as a function of the symbol boundary offset (normalized). For some accumulated lengths (shown as curves 410 and 415), the symbol boundary offset is a significant factor in the coherent accumulated energy normalized by energies varying up to 3 db. Is acting. For the third accumulated length (denoted as curve 405), the signal boundary offset has no significant effect on the normalized coherent accumulated energy.

  Obviously, for some accumulated lengths, the symbol boundary offset can change the amount of energy accumulated. Relatively large differences in accumulated energy may cause difficulties, for example, for communication systems using a transmit diversity scheme. In such a situation, the signal transmitted from one antenna will look significantly lower than the signal transmitted from the other antenna. This may make it difficult for the receiver to detect the presence of the antenna due to low accumulated energy.

  Referring now to FIG. 5, the received sequence 505 and some hypotheses 510 and 520 are illustrated in their symbol format, and the misalignment of the hypotheses with respect to the received sequence is illustrated. As shown in FIG. 5, receive sequence 505 is displayed as it is received, ie, in groups of N + 1 chips. For hypotheses 510 and 520, several groups of K + 1 chips are displayed. For hypotheses 510 and 520, the groups of K + 1 chips are shown as if they were generated by one sequence generator (not shown). However, due to differences in their PN offsets, the actual start (and completion) of the symbols in hypotheses 510 and 520 is different. For example, hypothesis 510 has a PN offset such that the symbols are aligned in a group of K + 1 chips, while hypothesis 520 defines a PN offset such that the symbols are unaligned in a group of K + 1 chips. Have. This misalignment is indicated by a symbol duration interval 525 that is slightly shifted to the right of the group of K + 1 chips representing hypothesis 520.

Now, note that due to the fact that the vectorized searcher is used to perform the correlation and that the vectorized searcher operates on K + 1 chips and K is 15, as a group of K + 1 chips: That is, the hypotheses 510 and 520 are displayed. Using non-vectorized searchers instead of vectorized searchers can eliminate the need to organize hypotheses 510 and 520 within a group of K + 1 chips. However, alignment and misalignment of correlations due to symbol boundaries still occur, and the present invention is still available. For example, the relationship of chip R [0] to chip C ^* [0] (from hypothesis 510) is symbol-aligned, while the relationship of chip R [0] to C ^* [-1] (from hypothesis 520) is Not aligned to symbol. However, the relationship of chip R [1] to C ^* [0] (from hypothesis 520) is symbol-aligned.

Because hypothesis 520 has boundary misalignment, the content of the group of K + 1 chips is labeled differently from the content of the K + 1 chip for reception sequence 505 and hypothesis 510. For example, the first group of K + 1 chips for hypothesis 510 is C ^* [0. . . K], while the first group of K + 1 chips for hypothesis 520 is C ^* [− 1. . . K−1] because the start of the group of K + 1 chips (chip 0) is actually the second chip in hypothesis 520. Thus, the correlation of received sequence 505 with hypothesis 520 (and subsequent accumulation) is non-aligned.

ここで、ｘ（）は、相関結果であり、ｒ（）は、受信シーケンスであり、ｃ^＊（）は、仮説であり、τは、相関オフセット（ＰＮオフセット）である。この相関は、表現される通りに遂行され、単一の受信シーケンスと複数の発生されたＰＮシーケンスとの相関を可能にする。 This correlation can be expressed mathematically as:

Here, x () is a correlation result, r () is a reception sequence, c ^* () is a hypothesis, and τ is a correlation offset (PN offset). This correlation is performed as expressed, allowing correlation of a single received sequence with multiple generated PN sequences.

  To ensure that the correlation (and thus the accumulation) is aligned along symbol boundaries, two conditions must be met. The first condition specifies that the length of the correlation (and accumulation) must be an integer multiple of the symbol period or duration. The second condition specifies that correlation (and accumulation) must start at the beginning of a symbol. The first condition can be fully satisfied through the correct specification of correlations and hypotheses. The second condition requires a modification to the way the correlation is performed.

）は、次のように書き直すことができる：

。そうした仕方で表現した場合、相関のあいだじゅう整列を維持することは、容易に遂行できる。書き直したようにこの相関は、単一の仮説により相関のために必要なよりも多く受信シーケンスの多数のチップを受信することにより、遂行される。それから、仮説（仮説６１０または６２０など）を供給されると、受信シーケンス６０５から適当なチップが選択されて仮説と相関される。たとえば、図６において、仮説６１０のＰＮオフセットのために、仮説６１０から発生されたＰＮシーケンスは、受信シーケンスのチップ０ないしチップＫと相関される。しかしながら、仮説６２０の場合は、信号境界との整列を維持するために、受信シーケンスのチップ１ないしチップＫ+１が、仮説６２０から発生されたＰＮシーケンスと相関される。 Referring now to FIG. 6, a schematic diagram illustrating a receiving sequence 605 and some hypotheses 610 and 620 according to a preferred embodiment of the present invention is shown, wherein the correlation between the hypotheses 610 and 620 and the receiving sequence 605 is different. Ensuring that signal alignment is maintained. The prior art correlation discussed above (in mathematical terms,

) Can be rewritten as:

. When expressed in such a manner, maintaining alignment throughout the correlation is easily accomplished. As rewritten, this correlation is accomplished by receiving a larger number of chips of the received sequence than needed for correlation by a single hypothesis. Then, given a hypothesis (such as hypothesis 610 or 620), an appropriate chip is selected from the receive sequence 605 and correlated with the hypothesis. For example, in FIG. 6, because of the PN offset of hypothesis 610, the PN sequence generated from hypothesis 610 is correlated with chips 0 through K of the received sequence. However, in the case of hypothesis 620, chips 1 through K + 1 of the received sequence are correlated with the PN sequence generated from hypothesis 620 to maintain alignment with the signal boundaries.

  According to a preferred embodiment of the present invention, the correlation technique outlined in FIG. 6 allows the receiver to receive more chips of the received sequence than is actually needed to perform the actual correlation. May be required. For example, using a vectorized searcher with a correlation length of 16 chips, it is necessary for the receiver to store the received sequence of 31 chips. The 31 chips are needed to support the worst-case situation of a hypothesis where the correlation of one hypothesis has a PN offset starting from the last chip (R [15]) of the 16-chip received sequence. With the correlation starting from R [15], 15 additional chips are then needed to complete the correlation, for a total of 31 chips. If this hypothesis has its correlation starting at the 17th chip (R [16]), then it can actually be performed by wrapping the received sequence back to R [0]. With a sequential searcher that correlates one chip at a time, 31 chip buffers are not required for a chip, but rather one chip buffer.

  Referring now to FIG. 7, there is shown a schematic diagram illustrating a portion of a wireless receiver 700 used to search for a direct sequence spread spectrum signal in accordance with a preferred embodiment of the present invention. This portion of the wireless receiver 700 used to search for the direct sequence spread spectrum signal uses the modified correlation method disclosed in FIG. 6 to perform signal alignment between the received signal and the hypothesis. Can be correlated. This part of the radio receiver 700 used for searching includes a searcher 705, a radio frequency (RF) section 720, a search control unit 725, a hypothesis memory 730 and a sequence generator 735.

  This searcher 705 can be used to perform the actual search on the direct sequence spread spectrum signal. Similar to a typical searcher implementing the correlation technique disclosed in FIG. 5, the searcher 705 receives a locally generated version of the chip (adjusted by a particular offset) in the descrambler 713. The search is performed by first correlating the chips from the sequence performed. For example, in the case of a pilot channel search, the searcher 705 uses a locally generated version of the PN sequence transmitted on the pilot channel (again, after being adjusted by a particular offset). ), Correlate with the received pilot channel. After correlation, the searcher 705 performs both coherent and non-coherent accumulation of the correlation result in a coherent / non-coherent accumulator 715. Finally, the accumulation is processed by the result processor 717. As an example of the operation of result processor 717, the accumulation performed in coherent / non-coherent accumulator 715 is compared against a predefined threshold in result processor 717. Hypotheses with accumulations that exceed a predefined threshold are determined to be good hypotheses and are saved, while hypotheses with accumulations that do not exceed a predefined threshold are removed. Good hypotheses are stored in memory for later use.

  The searcher 705 includes a sample buffer 709, which is used to store samples of the chip in the received signal used in subsequent correlations. A multiplexer 711 is used to select a subset of the samples of the received signal to be correlated. For example, if 31 chips use a sample buffer of 16 chip length correlation, then multiplexer 711 would be a 31-16 multiplexer, or a multiplexer that can select 16 chips from the 31 chip buffer. Searcher 705 also includes an acquisition time unit 707, which may be responsible for providing timing information based on local time at wireless receiver 700 and timing information derived from the received signal.

  Radio frequency (RF) section 720 includes an RF control interface 724 and a time base controller 722 to control RF hardware used to receive signals transmitted over the air to radio receiver 700. Used for The RF section 720 then provides the received signal to the searcher 705, preferably in the form of two sequences (I-sequence, Q-sequence) along with the timing reference signal.

  The searcher control unit 725 provides the necessary control information to the searcher 705 so that the searcher 705 can correlate the correct chip from the received sequence with the appropriate PN sequence generated from various different hypotheses. To ensure. The searcher control unit 725 searches the hypothesis memory 730 for a hypothesis to be tested. According to a preferred embodiment of the present invention, hypothesis memory 730 stores the hypotheses in sets of search parameters, where one set of search parameters defines one or more hypotheses. These sets of parameters, when combined with a timing reference (supplied by acquisition time unit 707), are used to generate the actual hypothesis to be tested. The hypothesis to be tested is then provided to a sequence generator 735. Sequence generator 735 then generates a PN sequence based on the hypothesis.

  Each hypothesis, in addition to being used to generate a PN sequence in sequence generator 705, is provided to a multiplexer 711 to provide the appropriate chip sample from the received sequence stored in sample buffer 709. Used to select a subset. Correlated with the PN sequence provided by sequence generator 735 is a subset of this chip sample from multiplexer 711.

  Referring now to FIG. 8, a schematic diagram illustrating a wireless device 800 according to a preferred embodiment of the present invention is shown. Wireless device 800 includes an analog front end 810 that receives signals transmitted over the air and detected by antenna 805. The analog front end 810 filters the received signal to remove out-of-band noise and interference, helps equalize and amplify the received signal, bring the received signal to a power level suitable for processing, and the like. used. An analog-to-digital converter (ADC) 815 is used to convert the analog received signal to its digital representation.

  The digital signal generated by ADC 815 is then provided to digital signal processing unit 820. This digital signal processing unit is responsible for functions such as error detection and correction of digital symbols, decoding and despreading of symbol streams, and deinterleaving and depuncturing of symbol streams. Memory 825 is used to store some or a portion of the symbol stream, data decoded from the symbol stream, search hypotheses, used as scratch memory, and so on. The searcher 705 (including the searcher control unit) and the sequence generator 703 are as described in FIG. Connecting these units together is a high speed communication bus 830.

  Referring now to FIG. 9, there is shown a flowchart illustrating an algorithm 900 used to ensure alignment of correlation and accumulation along symbol boundaries, in accordance with a preferred embodiment of the present invention. According to a preferred embodiment of the present invention, algorithm 900 is implemented in a searcher control unit (such as searcher control unit 725 (FIG. 7)). According to a preferred embodiment of the present invention, algorithm 900 operates in real time. Thus, the algorithm 900 is typically implemented on a custom designed integrated circuit or firmware to provide adequate performance. Alternatively, algorithm 900 may be implemented on a mobile control unit (MCU) (not shown), which operates on various portions of the wireless device if the MCU has sufficient processing power to provide real-time operation. Responsible for the control of

Upon receiving the hypothesis (or hypotheses), the searcher control unit 725 begins executing the algorithm 900 (block 905). This hypothesis is stored in the form of search parameters in a hypothesis memory (such as hypothesis memory 730 (FIG. 7)) and then combined with the timing reference to generate one or more hypotheses. Alternatively, the hypotheses may simply be stored in hypothesis memory 730 as a single hypothesis. After receiving this hypothesis, the searcher control unit 725 may determine a time index (block 910). According to a preferred embodiment of the invention, the time index for a given hypothesis is the time index modulo the code length. The time-stamp minus the hypothesis offset modulo the code length.

Then, the searcher control unit 725 determines a start condition and starts correlation and coherent accumulation (block 915). The desired start condition is expressed as when the time index is equal to zero (zero modulo the symbol length) modulo the symbol length. In other words, the desired start condition is when the time index is an integer multiple of the symbol length. For example, if the power of the symbol length (N) is 2, then the time index _{t m t m-1 t m} -2. . . If it can be expressed as t ₁ t ₀ , t _n−1 , t _n−2 ,. . . , T ₀ are all equal to 0 (where n = log ₂ N). The searcher control unit 725 also determines conditions for terminating coherent accumulation (block 920). A desirable condition for terminating coherent accumulation can be expressed as symbol length-16 modulo symbol length modulo the symbol length, where 16 is the length of the partial correlation. Referring back to the example where the symbol length is a power of two, the preferred condition for terminating coherent accumulation is when t _n−1 , t _n−2 are all equal to one (where , N = log ₂ N). Note that in situations where the symbol length is not a power of two, combinatorial logic can be used to indicate start and end conditions. The use of combinatorial logic to enforce start and end conditions is not discussed here because it is well understood by those of ordinary skill in the art of the present invention.

  The searcher control unit 725 then selects the desired chip sample from a sample buffer (such as sample buffer 709 (FIG. 7)) (block 925). According to a preferred embodiment of the present invention, searcher control unit 725 provides information to a multiplexer (such as multiplexer 711 (FIG. 7)), which causes multiplexer 711 to output the desired chip buffer from sample buffer 709. Choose a sample. After the desired chip sample has been selected (block 925), the searcher control unit 725 waits until the desired start condition is satisfied (block 930). Once the desired starting conditions are met, a hypothesis is assigned to the correlator (block 935) and testing of the hypothesis can begin.

  According to a preferred embodiment of the present invention, if the accumulation time L is an integer multiple of the symbol length N, ie, L = kN, where k is an integer, and then the correlator has k positions. The correlation can be started at any one of the following. This results in requiring one counter in each correlator.

  According to another preferred embodiment of the invention, when the accumulation time L is an integer multiple of the symbol length N, a correlation is forced to occur on one accumulation boundary. Since L = kN, the symbol alignment is trivially obtained (0 modulo L == 0 modulo N). Thus, the need to have a counter in each correlator can be eliminated at the expense of increased latency delay for initiating correlation.

  Having described the invention and its advantages in detail, it will be understood that various changes, substitutions and substitutions may be made herein without departing from the spirit and scope of the invention as defined in the appended claims. Should.

  Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As will be readily appreciated by one of ordinary skill in the art from the present disclosure, processes, machines that substantially accomplish the same function, or substantially achieve the same result, as the corresponding embodiments described herein. Anything that actually exists or is to be developed later in the manufacture, construction, means, method or steps of matter can be used by the present invention. Therefore, the appended claims are intended to include within their scope such processes, machines, manufacture, features of matter, means, methods, or steps.

The benefit of U.S. Provisional Patent Application No. 60 / 415,212, filed October 1, 2002, entitled "Method and Apparatus for Performing Symbol Alignment Search of DS SS Signals" is claimed and incorporated herein by reference.
(Cross-reference of related applications)

  This application is related to a commonly assigned patent application, filed on Aug. 28, 2003, entitled "Direct Sequence Sequence Using Pipelined Vector Processing," filed Aug. 28, 2003. Application No. XX-XXXXXX filed Aug. 28, 2003, entitled "System and Method for Detecting Multiple Direct Sequence Spread Spectrum Signals Using a Multi-Mode Searcher" filed on Aug. 28, 2003. Application No. 10 / 439,400, filed May 16, 2003; "System and method for intelligent processing of results from searching direct sequence spread spectrum (DSSS) signals; Application No., filed August 28, 2003; XX-XXXXXX name "direct sequence specification using batch processing of independent variables" System and method for detecting a tram spread signal ", the disclosure of these various applications, herein incorporated herein.

For a more complete understanding of the present invention and its advantages, the foregoing description has been set forth in conjunction with the accompanying drawings.
1 is a schematic diagram of an exemplary wireless communication system. 3 is a timing chart of several bit periods of a signal in a direct sequence spread spectrum communication system. FIG. 4 is a timing chart of a modulation pattern of a direct sequence spread spectrum communication system using transmit antenna diversity. 4 is a data plot of normalized coherent accumulated energy as a function of normalized accumulated offset for a direct sequence spread spectrum communication system using transmit antenna diversity displayed in FIG. 5 is a schematic diagram of a received sequence and some hypotheses, wherein the misalignment of hypothesis correlation with the received sequence is highlighted. Fig. 4 is a schematic diagram of several hypotheses of one received sequence, with the correlation modified to prevent misalignment of the hypotheses with respect to the received sequence according to a preferred embodiment of the present invention. 4 is a schematic diagram of a portion of a wireless receiver used to search for a direct sequence spread spectrum signal in accordance with a preferred embodiment of the present invention. 1 is a schematic diagram of a wireless device according to a preferred embodiment of the present invention. 5 is a flowchart of an algorithm used to ensure correlation alignment and accumulation along signal boundaries according to a preferred embodiment of the present invention.

Explanation of reference numerals

605 Receive sequence 610, 620 Hypothesis 700 Radio receiver 705 Searcher 707 Acquisition time unit 709 Sample buffer 711 Multiplexer 713 Descrambler 715 Coherent / non-coherent accumulator 717 Result processor 720 Radio frequency (RF) section 722 Time base controller 724 RF control interface 725 Search control unit, searcher control unit 730 Hypothesis memory 735 Sequence generator 800 Wireless device 805 Antenna 710 Analog front end 815 Analog to digital converter (ADC)
820 Digital signal processing unit 830 High-speed communication bus

Claims (10)

Receiving the hypothesis,
Determining start and end conditions;
Selecting a sample from a received sequence based on the start condition;
Providing the samples and hypotheses to a correlator.
How to test hypotheses by symbol alignment correlation.   The method of claim 1, wherein the start condition is expressed as when a time index according to modulo N is equal to zero, and N is the length of a symbol. A N is a power of two, if the time index is expressed as _{t m t m-1 t m} -2 ... t 1 t 0, t n-1, t n-2,. .., t _m-0 is equal to zero, n = l0g a ₂ n, method of claim 2 wherein.   The termination condition is expressed when the time index is equal to (N-partial correlation length) by modulo N, where N is the length of the symbol and the correlation length is the number of chips to be correlated. The method of claim 1. After supplying the samples and hypotheses to the correlator,
Generating a pseudo-random sequence based on said hypothesis;
Correlating the pseudo-random sequence with the samples;
Accumulating the correlation result;
5. The method according to claim 1, further comprising processing the accumulation result. A search control unit coupled to a hypothesis memory, the search control unit including circuitry for providing correlation start and stop conditions based on hypotheses read from the hypothesis memory;
A searcher coupled to the search control unit, wherein the searcher selects a subset of samples from a received sequence based on instructions from the search control unit, and correlates the subset of samples with a pseudo-random sequence; The searcher including a circuit for accumulating the correlation result;
A sequence generator coupled to the search control unit and the searcher, the circuit including a circuit for generating the pseudo-random number sequence based on the hypothesis. A multiplexer coupled to a receive sequence input, said multiplexer comprising circuitry for selecting said subset of samples from said receive sequence based on start and stop conditions provided by said search control unit;
A descrambler coupled to the multiplexer and the sequence generator, the descrambler including circuitry for correlating the subset of samples from the multiplexer with the pseudo-random sequence from the sequence generator;
7. The circuit of claim 6, wherein the searcher includes an accumulator coupled to the descrambler, the accumulator including circuitry for coherently and non-coherently accumulating the correlation result.   The circuit of claim 6 or claim 7, wherein the hypotheses stored in the hypothesis memory are stored as a set of search parameters, and the hypotheses are derived from the set of search parameters and a timing reference. . An analog front end coupled to an antenna, the analog front end including circuitry for filtering and amplifying a received signal provided by the antenna;
An analog-to-digital converter (ADC) for converting an analog signal provided by the analog front end into a digital signal stream;
A search unit coupled to the ADC, the search unit including a test circuit, wherein the test is performed along a symbol boundary;
A wireless device comprising: a processing unit coupled to said ADC, said processing unit including circuitry for error detecting and correcting, decoding, despreading, and filtering said digital symbol stream. A search control unit coupled to a hypothesis memory, the search control unit including circuitry for providing start and stop conditions for correlation based on a hypothesis read from the hypothesis memory;
A searcher coupled to the search control unit, wherein based on instructions from the search control unit, selecting a subset of samples from a received sequence and correlating the subset of samples with a pseudo-random sequence; The searcher including a circuit for accumulating the result of the correlation;
10. The wireless device of claim 9, wherein the search unit includes a sequence generator coupled to the search control unit and the searcher, the sequence generator including circuitry for generating a pseudo-random sequence based on the hypothesis.

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